Method and system for improved sonet data communications channel

ABSTRACT

Systems and methods for use in a synchronous network in which the line data communications channel and section data communications channel are combined to provide an increased bandwidth data communication channel. In one aspect of the invention, all of the bytes of the line data communications channel are combined with the bytes of the sections data communications channel to create a single data communications channel. In another aspect, some but not all of the line data communications channel bytes are moved to the sections data communications channel in order to create an increased capacity section data communications channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/094,415, filed Jul. 28, 1998, the contents of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to the transmission of data in asynchronous optical network, and more particularly, to an overheadstructure for a data frame in a synchronous optical network.

A standard known as Synchronous Optical Network (SONET) defines ahierarchy of rates and formats for use in optical communicationssystems, as well as other systems. The CCITT has adopted a similarstandard and named it the Synchronous Digital Hierarchy (SDH). TheSONET/SDH standard is expected to provide a worldwide telecommunicationsinfrastructure for transmitting information. The terms SONET and SDHwill henceforth be used interchangeably. Although, there are smalldifferences between the two formats, the differences are immaterial forthe present invention.

As shown in FIG. 1, there are three layers in the SONET architecture.These layers include a section, a line, and a path. A section concernscommunications between two adjacent network elements, referred to as asection terminating equipment (STE) 110-1 through 110-6. Regenerators140-1 and 140-2 and add-drop multiplexers (ADM) 150-1 and 150-2 areexamples of STE 110-3, 110-4, 110-2, and 110-5, respectively.

A line concerns communications between line terminating equipment (LTE)120-1 through 120-4, such as add-drop multiplexers 150. As shown in FIG.1, a line includes one or more sections. LTEs 120-1 through 120-4perform line performance monitoring and automatic protection switching.Regenerators generally are not LTEs, although add-drop multiplexerstypically are both an STE and an LTE.

An end-to-end connection is called a path and the equipment on eitherend that sends or receives a signal is called a path-terminatingequipment (PTE). As shown in the FIG. 1, a path includes one or morelines which in turn include one or more sections.

SONET uses a basic transmission rate of STS-1, which provides a datarate of 51.84 Mbps. Higher rate SONET signals are integer multiples ofthis base rate. For example, an STS-3 has a data rate of 155.52 Mbps, or3×51.84 Mbps.

The frame format of the STS-1 is shown in FIG. 2. The frame 210 isdivided into two protions: transport overhead 220 and a synchronouspayload envelope (SPE) 230. The SPE 230 is an 87 column by 9 row matrix,for a total of 783 bytes, and is divided into two parts: the STS pathoverhead 232 and the payload 234. The transport overhead 220 is dividedinto section overhead 222 and line overhead 224.

FIG. 3, provides a diagram of the transport overhead for the currentSONET frame structure. In the current frame structure, the first threerows of the transport overhead contain the section overhead and thefinal six rows contain the line overhead.

The following table provides a brief description of the section overhead222 bytes shown in FIG. 3. Byte Description A1 and A2 Framing Bytes -These bytes indicate the beginning of an J0/Z0 STS-1 frame Section Trace(JO)/Section Growth(ZO) - In an STS-N frame, this byte is either thesection trace byte, if the STS-1 frame is the first STS-1 frame in theSTS-N frame, or is the section growth byte, if the STS-1 frame is thesecond through Nth STS-1 frame in the STS-N frame. This byte wasformerly defined as the STS-1 ID (C1) byte. B1 Section bit interleavedparity code (BIP-8) byte - This is a parity code (even parity) forchecking for transmission errors over a section. In an STS-N frame, thisbyte is defined for only the first STS-1 frame E1 Section orderwirebyte - This byte is used as a local orderwire channel for voicecommunications between regenerators, hubs, and remoter terminallocations F1 Section user channel byte - This byte is set aside for theuser. It terminates at all STEs within a line. D1, D2, D3 Section datacommunications channel (DCC) bytes - These bytes form a 192 kbps messagechannel providing a message-based channel for operations,administration, maintenance, and provisioning (OAM&P) between STEs. Thischannel is used from a central location for alarms, control, monitoring,administration and other communications needs. It is available forinternally generated, externally generated, or manufacturer-specificmessages.

The following table provides a brief description of the line overhead224 bytes shown in FIG. 3. Byte Description H1, H2 STS payload pointer -These pointer bytes are used in frame alignment and frequencyadjustment. H3 Pointer action byte - This byte is used for SPE frequencyjustification. It is used in all STS-1 frames within an STS-N frame tocarry an extra SPE byte in the event of a negative pointer adjustment.When it is not used to carry the SPE byte this byte is undefined. B2Line bit interleaved parity code byte - This byte is used to determineif a transmission error has occurred over the line. K1, K2 Automaticprotection switching (APS channel) bytes - These bytes are used forprotection signalling between LTEs for bi- directional APS and fordetecting alarm indication signals (AIS-L) and remote defect indication(RDI) signals. D4-D12 Line data communications channel bytes (LDCC) -These 9 bytes are used to provide a 576 kbps message channel from acentral location for OAM&P information, such as alarms, control,maintenance, remote provisioning, monitoring, administration, and othercommunications needs, between LTEs. This channel is available forinternally generated, externally generated and manufacturer-specificmessages. S1 Synchronization status byte - This byte is located in thefirst STS-1 frame in an STS-N frame. Bits 5-8 of this byte convey thesynchronization status of the network. Z1 Growth byte - This byte isallocated in the 2^(nd) through N^(th) STS-1 frame in an STS-N framewhere 3 ≦ N ≦ 48, and is allocated for future growth. M0 STS-1 REI-Lbyte - This byte is only defined for an STS-1 frame in an OC-1 or STS-1electrical signal. Bits 5-8 of this byte are allocated for a line remoteerror indication function (REI-L), formerly referred to as Line FEBE.This function conveys the error count detected by an LTE, using the lineBIP-8 code, back to its peer LTE. M1 STS-N REI-L byte - This byte islocated in the third STS-1 frame in an STS-N frame, and is used forREI-L purposes. Z2 Growth byte - This byte is located in the first andsecond STS-1 frame of an STS-3 frame and the first, second, and fourththrough N^(th) STS-1 frame of an STS-N frame, where 12 ≦ N ≦ 48. Thesebytes are allocated for future growth. E2 Orderwire byte - This byteprovides a 64 kbps channel between LTEs for an express orderwire. It isa voice channel for use by technicians.

SONET standards have specified a number of management applications whoseprotocol data units (PDU) are characterized by their large size. Theseapplications include the common management information protocol (CMIP)based Open Systems Interconnection (OSI) management (X.711 or ISO 9596),the file transfer access management (FTAM) based software download andremote back-up applications (ISO 85714), X.500 based directory services,and T1.245 compliant registration management.

Presently, these applications are assigned to the 192 kbps Section DataCommunications Channel (SDCC) channel. Because of the large applicationmessage size, the total traffic from these applications will exceed thecapacity of the SDCC for all but the very simplest SONET networks.

In addition to problems with capacity, there are problems with thecurrent transport overhead structure due to lack of prioritization.Presently, there is no priority mechanism for determining whichinformation can be discarded when the SDCC channel is overloaded.Therefore, in the event the capacity of the SDCC channel is exceeded,information is discarded without any intelligent discrimination. Thiscan result in the loss of vital messages and lead to network failures.

In addition, a number of protocol entities within the OSI seven layercommunications stack serving the SDCC conduct peer-to-peercommunications over the SDCC, consuming bandwidth that would otherwisebe available to management applications. During steady state conditionsthis protocol traffic is low, however, during abnormal conditions, thistraffic can rise to a level that may result in application or protocoltraffic being discarded, and thus could lead to network failures.

In addition, the current structure of the transport overhead requiresunnecessarily complex SONET interfaces. The current separation of theSONET DCC into SDCC and Line Data Communications Channel (LDCC) requireseach SONET interface (that is, both STE and LTE) to terminate an inboundand an outbound SDCC and an inbound and outbound LDCC, for a total offour point to point links per interface. Each of these four links mustbe brought to a time slot interchange (TSI) for purposes of forwardingor connection to the data link layer of the OSI stack. As such, the TSIsfor use with the current overhead structure are unnecessarily complex.FIG. 4 provides an illustration of a TSI 410 of the prior art and showsthat TSI 410 receives and transmits information on both the SDCC andLDCC. As such, TSI 410 must drop both the SDCC and LDCC for everyinterface.

Furthermore, at present the LDCC is under-utilized. This is because,despite its bandwidth being triple that of the SDCC, standards have notassigned any management applications to the LDCC.

SUMMARY OF THE INVENTION

Thus, it is desirable to have a method and system for an improved SONETData Communications Channel, which overcomes the above and otherdisadvantages of the prior art.

Methods and systems consistent with the present invention include aframe for carrying information over a communications channel thatincludes a section overhead and a line overhead. In this aspect, LDCCbytes of the transport overhead are eliminated and added to the SDCCbytes, thus increasing the capacity of the SDCC.

In accordance with one embodiment, such methods and systems comprise anetwork, including LTEs and STEs. In this aspect, the LTEs and STEsinclude a framer that inserts a greater number of data communicationschannel bits into the section overhead than into the line overhead, thusincreasing the capacity of the SDCC over the prior art.

In accordance with another embodiment, such methods and systems comprisea network element that inserts a greater number of data communicationschannel bytes into the section overhead than the, line overhead, thusincreasing the capacity of the SDCC over the prior art.

In another aspect, the invention comprises a dual mode adapter thatincludes means for inserting data communications channel bytes into aframe with a higher capacity SDCC, means for inserting datacommunications channel bytes into a frame according to the prior art,and means for selecting between these two means.

The summary of the invention and the following detailed descriptionshould not restrict the scope of the claimed invention. Both provideexamples and explanations to enable others to practice the invention.The accompanying drawings, which form part of the description forcarrying out the best mode of the invention, show several embodiments ofthe invention, and together with the description, explain the principlesof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Figures:

FIG. 1 is an illustration of a SONET architecture;

FIG. 2 is an illustration of a SONET frame;

FIG. 3 is an illustration of a prior art transport overhead structure;

FIG. 4 is a block diagram of a prior art time slot interchange;

FIG. 5 is a block diagram of an add drop multiplexer, in accordance withmethods and systems consistent with the invention;

FIG. 6 is an illustration of a transport overhead structure, inaccordance with methods and systems consistent with the invention;

FIG. 7 is an illustration of a transport overhead structure, inaccordance with methods and systems consistent with the invention;

FIG. 8 is a block diagram of a framer, in accordance with methods andsystems consistent with the invention;

FIG. 9 is a flow diagram illustrating a process for constructing anSTS-1 frame with an overhead structure consistent with the prior artSONET standards;

FIG. 10 is a flow diagram illustrating a process for constructing anSTS-N frame with an overhead structure consistent with the prior artSONET standards;

FIG. 11 is a flow diagram illustrating a process for constructing anSTS-1 frame with an overhead structure in which the LDCC bytes areeliminated, in accordance with systems and methods consistent with theinvention;

FIG. 12 is a flow diagram illustrating a process for constructing anSTS-1 frame with an overhead structure in which the SDCC is larger thanthe LDCC, in accordance with systems and methods consistent with theinvention;

FIG. 13 is a block diagram of a time slot interchange, in accordancewith methods and systems consistent with the invention; and

FIG. 14 is a block diagram of a dual mode adapter, in accordance withmethods and systems consistent with the invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 5 provides a more detailed diagram of an ADM 150, such asillustrated in FIG. 1. The functional elements of ADM 150 may includeSTE 110, LTE 120, a framer 510, a de-framer 520, a payload processor530, a time slot interchange (TSI) 540, and a management processor 550.

In a preferred embodiment, the line data communications channel bytes ofthe transport overhead are eliminated and combined with the section datacommunications channel bytes, thus creating a single SDCC of 12 bytesand 768 kbps capacity. FIG. 6 illustrates a transport overheadconsistent with the present invention. Data communications channel bytesD4 thru D12 are moved from the line data communications channel in theprior art transport overhead structure, which is shown in FIG. 3, intothe section data communications channel to create a single datacommunications channel. Thus, the resulting data communications channelconsists of 12 bytes and provides a 768 kbps channel.

In another embodiment, some, but not all of the LDCC bytes are combinedwith the SDCC bytes, as shown in FIG. 7, to create a larger SDCC. InFIG. 7, the SDCC includes DCC bytes D1-D9, while the LDCC includes DCCbytes D10-D12. This results in a SDCC with a capacity of 576 kbps and aLDCC with a capacity of 192 kbps.

FIG. 8 shows a block diagram of a framer 510 in accordance with anembodiment of the present invention. As shown, framer 510 includes meansfor inserting payload into a SONET frame 810, and a means for insertingoverhead into the SONET frame 820. In general, framers are very complexand include many data mappings, dependencies on the STS-N signal rate(e.g., STS-1, STS-3, etc), and payload position variations based onpointers. However, much of this complexity has no bearing on the DataCommunications Channel (DCC), and the following description of a framerof a preferred embodiment is accordingly limited.

For an STS-1 signal, a prior art SONET framing device inserts the threesection DCC bytes in the standards-defined position of row 3, columns 1,2, and 3, as illustrated in FIG. 3. Thus, the three SDCC bytes occupythree consecutive bytes whose absolute byte location within the frameare 181, 182, and 183 (where the absolute byte location is determined byconsecutively numbering the bytes starting with row 1 column 1), becausethe first three rows of the frame are 90 bytes. As such, the first byteof the third column of the frame is byte 181 (row 1: 90 bytes+row 2: 90bytes=180 bytes). Similarly, the LDCC occupies, as defined by the SONETstandards, the row 6 columns 1 through 3, row 7 columns 1 through 3, androw 8 column 1 through 3, as shown in FIG. 3. In terms of absolute bytelocation, the LDCC thus occupies bytes 451 through 453, 541 through 543,and 631 through 633.

For an STS-N frame, the DCC bytes are defined only for the first STS-1of the frame. As such, in frames with a rate higher than STS-1, the DCCbytes are non-consecutive because the corresponding byte positions inthe STS-Ns are undefined. Thus, in an STS-3 frame, which has 270 byterows, the D1 byte occupies the first column of row 3 as is the case withan STS-1, but D2 is in the fourth column of row 3 and D3 is in theseventh column of row 3. The intervening bytes (part of STS #2 and STS#3) between the DCC bytes, the 2^(rd), 3^(rd), 5^(th), 6^(th), 8^(th),and 9^(th) columns of row three are empty. Thus, the three section DCCbyte locations are the 541^(st) (D1), 544^(th) (D2), and 547^(th) (D3)bytes of the frame.

FIG. 9 illustrates a flow chart of an algorithm that can be used forconstructing an STS-1 SONET frame according to the transport overheadstructure defined by today's SONET standards, as shown in FIG. 3. Asillustrated, a framer inserts bits into the frame one row at a time.First row 1 is inserted, which includes framing bytes A1 and A2, STSidentifier byte C1, and 87 bytes of payload data and path overhead(S902). Then the second row is inserted, which includes bytes B1, E1,F1, and 87 bytes of payload data and path overhead (S904). The third rowthat includes bytes D1, D2, D3, and 87 bytes of payload data and pathoverhead is then inserted (S906). After which, the fourth row thatincludes bytes H1, H2, H3, and 87 bytes of payload data and pathoverhead is inserted (S908). Then, the fifth row that includes bytes B2,K1, K2, and 87 bytes of payload data and path over head is inserted(S910). The sixth row that includes bytes D4, D5, D6, and 87 bytes ofpayload data and path overhead is then inserted (S912). After which, theseventh row that includes bytes D7, D8, D9, and 87 bytes of payload dataand path overhead is inserted (S914). Then the eighth row that includesbytes D10, D11, D12, and 87 bytes of payload data and path overhead isinserted (S916). The ninth row that includes byte Z1, Z2, E2, and 87bytes of payload data and path overhead is then inserted (918). Thus,through this algorithm all 9 rows are inserted into the STS-1 frame.

As such, this process creates an STS-1 frame with the overhead structureof the prior art, in which SDCC bytes D1 -D3 are inserted into row 3 ofthe frame (S906), and LDCC bytes D4-D6 are inserted into row 6 (S912),LDCC bytes D7-D9 are inserted into row 7 (S914), and LDCC bytes D10-D12are inserted into row 8 (S916).

FIG. 10 illustrates a flow chart for a process that can be used tocreate a STS-N frame according to the transport overhead structuredefined by today's SONET standard. As illustrated, a framer inserts bitsinto the frame one row at a time. First, row 1 is inserted, whichincludes N A1 framing bytes, N A2 framing bytes, N C1 bytes, and N times87 bytes of payload data and path overhead (S1002). Then the second rowis inserted, which includes bytes B1, E1, F1, and N times 87 bytes ofpayload data and path overhead (S1004). The third row including bytesD1, D2, D3, and N times 87 bytes of payload data and path overhead isthen inserted (S1006). After which, the fourth row, which includes N H1bytes, N H2 bytes, N H3 bytes, and N times 87 bytes of payload data andpath overhead, is inserted (S1008). Then, the fifth row, which includesN B2 bytes, the K1 byte, the K2 byte, and N times 87 bytes of payloaddata and path overhead, is inserted (S1010). The sixth row, whichincludes bytes D4, D5, D6, and N times 87 bytes of payload data and pathoverhead, is then inserted (S1012). After which, the seventh row, whichincludes bytes D7, D8, D9, and N times 87 bytes of payload data and pathoverhead, is inserted (S1014). Then the eighth row, which includes bytesD10, D11, D12, and N times 87 bytes of payload data-and path overhead,is inserted (S1016). The ninth row, which includes N Z1 bytes, N Z2bytes, N E2 bytes, and N times 87 bytes of payload data and pathoverhead is then inserted (1018). Thus, through this algorithm all 9rows are inserted into the STS-N frame.

As such, the framer inserts SDCC bytes D1-D3 into row 3 of the STS-Nframe (S1006), LDCC bytes D4-D6 into row 6 (S1010), LDCC bytes D7-D9into row 7 (S1012), and LDCC bytes D10-D12 into row 8 (S1014).

As previously indicated, the SONET frame of a preferred embodiment hasan increased capacity SDCC. From a framing algorithm perspective, thereare no changes in the total number of bytes, rows, or columns that makeup the frame, nor is the total number of DCC bytes altered. This meansthat the changes to the framing algorithm, preferably, includere-ordering of the rows without changing how each row is sequenced. Thechanges also have no impact on the STS-N interleaving dependency either,i.e., the “N-1” and “N times 87” factors are unchanged.

In a preferred embodiment, all nine LDCC bytes are moved to the SDCC,totally eliminating the LDCC. In the resulting DCC shown in FIG. 6, thetwelve DCC bytes are placed in the first three columns of fourconsecutive rows beginning with row 3, the original starting row for theSDCC.

In accordance with an embodiment of the invention, the correspondingbyte positions are as follows for an STS-1 frame: D1-D3 Bytes 181-183D4-D6 Bytes 271-273 D7-D9 Bytes 361-363 D10-D12 Bytes 451-453

In this embodiment, overhead rows 4 and 5 of the frame structurecontaining the pointer, parity, and protection switching overhead bytes(H1-3, B2, K1-3) are repositioned intact to rows 7 and 8. Total lineoverhead is thus reduced from 6 rows by 3 columns or 18 bytes to 3 rowsby 3 columns or 9 bytes. The total number of section and line overheadbytes is not changed and remains at 27 (9 rows by 3 columns). The numberof section overhead bytes is increased from 9 bytes to a total of 18bytes.

FIG. 11 illustrates a flow chart of an algorithm that can be used forconstructing an STS-1 frame according to a transport overhead in whichall the LDCC bytes are eliminated and combined with the SDCC bytes tocreate a single DCC. As illustrated, a framer of this embodiment insertsbits into the frame one row at a time. First row 1 is inserted, whichincludes framing bytes A1 and A2, STS identifier byte C1, and 87 bytesof payload data and path overhead (S1102). Then the second row isinserted, which includes bytes B1, E1, F1, and 87 bytes of payload dataand path overhead (S1104). The third row that includes bytes D1, D2, D3,and 87 bytes of payload data and path overhead is then inserted (S1106).The fourth row that includes bytes D4, D5, D6, and 87 bytes of payloaddata and path overhead is then inserted (S1108). After which, the fifthrow that includes bytes D7, D8, D9, and 87 bytes of payload data andpath overhead is inserted (S1110). Then the sixth row that includesbytes D10, D11, D12, and 87 bytes of payload data and path overhead isinserted (S1112). After which, the seventh row that includes bytes H1,H2, H3, and 87 bytes of payload data and path overhead is inserted(S1114). Then, the eighth row that includes bytes B2, K1, K2, and 87bytes of payload data and path over head is inserted (S1116). The ninthrow that includes byte Z1, Z2, E2, and 87 bytes of payload data and pathoverhead is then inserted (S1118). Thus, through this algorithm all 9rows are inserted into the STS-1 frame.

As such, DCC bytes D1-D3 are inserted into row 3 of the frame (S1106),D4-D6 are inserted into row 4 (S1108), D7-D9 are inserted into row 5(S1110), and D10-D12 are inserted into row 6 (S1112).

As compared to the above described standardized algorithm for creatingan STS-1 frame illustrated in FIG. 9, this algorithm has the followingfive differences:

-   -   1. DCC bytes D4-D6 are inserted in row 4 columns 1-3 instead of        row 6 columns 1-3.    -   2. DCC bytes D7-D9 are inserted in row 5 columns 1-3 instead of        row 7 columns 1-3.    -   3. DCC bytes D10-D12 are inserted in row 6 column 1-3 instead of        row 8 columns 1-3.    -   4. Pointer Bytes H1-H3 are inserted in row 7 column 1-3 instead        of row 4 column 1-3.    -   5. The B2, K1, and K2 overhead bytes are inserted in row 8        column 1-3 instead of row 5 column 1-3.

A network element of a preferred embodiment may use the above describedtransport overhead structure to create a frame with a DCC but no LDCC.

In another embodiment, the capacity of the SDCC is increased at theexpense of the LDCC, without totally eliminating the LDCC, because itmay be desirable to retain a small amount of LDCC capability whileshifting the bulk of the LDCC capacity to SDCC.

FIG. 12 illustrates a flow diagram of an algorithm for constructing aframe in which the SDCC capacity is tripled by moving six of the nineLDCC bytes to the SDCC. As illustrated, a framer inserts bits into theframe one row at a time. First, row 1 is inserted, which includes bytesA1, A2, C1, and 87 bytes of payload data and path overhead (S1202). Thenthe second row is inserted, which includes bytes B1, E1, F1, and 87bytes of payload data and path overhead (S1204). The third row includingbytes D1, D2, D3, and 87 bytes of payload data and path overhead is theninserted (S1206). The fourth row, which includes bytes D4, D5, D6, and87 bytes of payload data and path overhead, is then inserted (S1208).After which, the fifth row, which includes bytes D7, D8, D9, and 87bytes of payload data and path overhead is inserted (S1210). Afterwhich, the sixth row, which includes bytes H1, H2, H3, and 87 bytes ofpayload data and path overhead is inserted (S1212). Then, the seventhrow, which includes bytes B2, K1, K2, and 87 bytes of payload data andpath overhead, is inserted (S1214). Then the eighth row, which includesbytes D10, D11, D12, and 87 bytes of payload data and path overhead, isinserted (S1216). The ninth row that includes bytes Z1, Z2, E2, and 87bytes of payload data and path overhead is then inserted (S1218). Thus,through this algorithm all 9 rows are inserted into the STS-1 frame.

As such, D10-D12 are the retained LDCC bytes and are inserted into row 8(S1216). Further, in this example, DCC bytes D1-D3 are inserted into row3 (S1206), D4-D6 are inserted into row 4 (S1208), and D7-D9 are insertedinto row 5 (S1210). As such, D4-D9 become the additional SDCC bytes.

The above description of the framer is but one possible implementationof a framer consistent with the invention. Those skilled in the art willunderstand that various changes and modifications may be made, andequivalents may be substituted for the above described preferredembodiments of the framer without departing from the true scope of theinvention.

Furthermore, a network element of a preferred embodiment may use theabove described tranport overhead structure to create a frame with moreSDCC bytes than LDCC bytes.

FIG. 13 illustrates a TSI 1300, for use in a network implementing aSONET frame comprising an SDCC, but no LDCC, in accordance with anembodiment of the invention. The TSI 1300 comprises only S dropchannels. Because there is no LDCC, only a single pair of inbound andoutbound SDCC point to point links must be terminated at each interface.Further, as will be obvious to one skilled in the art, the sameabove-described principals and possible improvements described for theTSI are equally applicable to any device that selectively, undersoftware control, allows input data slices to be transferred to outputports, while maintaining the integrity and timing of the data.

FIG. 14 illustrates a dual-mode adapter 1410 for use in a networkimplementing both a frame of a preferred embodiment of the invention anda frame with the existing SONET overhead structure, in accordance withan embodiment of the invention. This dual-mode adapter 1410 includesboth a legacy framer 1420 and a combined DCC framer 1430 in additiontoga selector 1440. The legacy framer 1420 constructs frames with theoverhead structure of the prior art, while the combined DCC framer 1430constructs frames with an increased capacity SDCC channel. The selector1440 selects whether to use the legacy framer 1420 or the combined DCCframer 1430.

A network according to a preferred embodiment may include STEs and LTEs.In this embodiment, the STEs and LTEs include a framer 800 as shown inFIG. 8. This framer 800, like the framers described above, creates aframe with more SDCC bytes than LDCC bytes. In one aspect of thisembodiment, all the LDCC bytes in the transport overhead of the priorart are eliminated and added to the SDCC bytes to create a transportoverhead structure such as is shown in FIG. 6. In another aspect, onlysome of the LDCC bytes are eliminated and combined with the SDCC bytes,thus creating an increased capacity SDCC, such as is shown in FIG. 7.

Referring back to FIG. 5, the de-framer 520 may include means forextracting payload bits from the frame and means for extracting overheadbits from the frame. The means for extracting payload bits and the meansfor extracting overhead bits may be implemented using software orhardware, such as application specific integrated circuit (ASIC). Aswill be obvious to one of skill in the art in light of the abovedescribed description, in one embodiment, the de-framer 520 may operateto extract SDCC bytes from a frame in which there is no LDCC. As such,in this embodiment, the de-framer 520 would not extract LDCC bytes.

While it has been illustrated and described what is at presentconsidered to be the preferred embodiment and methods of the presentinvention, it will be understood by those skilled in the art thatvarious changes and modifications may be made, and equivalents may besubstituted for elements thereof without departing from the true scopeof the invention.

In addition, many modifications may be made to adapt a particularelement, technique or, implementation to the teachings of the presentinvention without departing from the central scope of the invention.Therefore, it is intended that this invention not be limited to theparticular embodiment and methods disclosed herein, but that theinvention includes all embodiments falling within the scope of theappended claims.

1. A frame for carrying information over a communications channel,comprising: a payload envelope; and a transport overhead comprising,section overhead, and line overhead; wherein the section overheadcontains more space allocated to the section overhead for bitscorresponding to a data communications channel than line space allocatedto the line overhead.
 2. The frame of 1 wherein the line overhead has nodata communications channel bits.
 3. The frame of 1 wherein the frame isa SONET frame.
 4. The frame of 1 wherein the frame is an SDH frame.
 5. Amethod for creating a frame comprising the steps of: inserting a payloadinto the frame; inserting an overhead into the frame, including thesteps of inserting data communications channel bits into the overheadwherein the number of data communications channel bit inserted into asection overhead and space allocated to the section overhead is greaterthan the number of data communications channel bits inserted into a lineoverhead and space allocated to the line overhead.
 6. The method of 5wherein the number of data communications channel bits inserted into theline overhead is zero.
 7. The method of 5 wherein the frame is a SONETframe.
 8. The method of 5 wherein the frame is a SDH frame.
 9. A framer,comprising: means for inserting into a frame a payload; means forinserting into the frame a plurality of data communications channelbits, wherein the number of data communications channel bits insertedinto a section overhead and space allocated to the section overhead isgreater than the number of data communications channel bits insertedinto a line overhead and space allocated to the line overhead.
 10. Theframer of claim 9 wherein the number of data communications channel bitsinserted into the line overhead is zero.
 11. The framer of claim 9wherein the frame is a SONET frame.
 12. The framer of claim 9 whereinthe frame is a SDH frame.
 13. A network, comprising: a plurality of lineterminating equipment, comprising means for inserting into a frame apayload, means for inserting into the frame a plurality of datacommunications channel bits, wherein the number of data communicationschannel bits inserted into a section overhead and space allocated to thesection overhead is greater than the number of data communicationschannel bits inserted into a line overhead and space allocated to theline overhead; and a plurality of section terminating equipment,comprising means for inserting into a frame a payload, means forinserting into the frame a plurality of data communications channelbits, wherein the number of data communications channel bits insertedinto a section overhead and space allocated to the section overhead isgreater than the number of data communications channel bits insertedinto a line overhead and space allocated to the line overhead.
 14. Thenetwork of claim 13 wherein the number of data communications channelbits inserted into the line overhead is zero.
 15. The network of claim13 wherein the frame is a SONET frame.
 16. The network of claim 13wherein the frame is an SDH frame.
 17. The network of claim 13 whereinone of the plurality of line terminating equipment is an add-dropmultiplexer.
 18. The network of claim 13 wherein one of the plurality ofsection terminating equipment is a regenerator.
 19. The network of claim13 wherein one of the plurality of line terminating equipment is adigital cross-connect.
 20. The network of claim 13 wherein one of theplurality of line terminating equipment an ATM over SONET networkelement.
 21. A method for extracting overhead information from a frame,comprising the steps of: locating in the frame a plurality of datacommunications channel bits; extracting a plurality of datacommunications channel bits from a section overhead without extractingdata communications channel bits from a line overhead.
 22. The method of21 wherein the frame is a SONET frame.
 23. The method of 21 wherein theframe is an SDH frame.
 24. A time slot interchange, comprising means forlocating a plurality of data communications channel bits in a frame;means for extracting a plurality of data communications channel bitsfrom a section overhead without extracting data communications channelbits from a line overhead.
 25. The time slot interchange of claim 24wherein the frame is a SONET frame.
 26. The time slot interchange ofclaim 24 wherein the frame is an SDH frame. 27-30. (canceled)
 31. Anetwork element, comprising: means for inserting into a frame aplurality of payload bits; and means for inserting into the frame aplurality of data communications channel bits, wherein the number ofdata communications channel bits inserted into a section overhead andspace allocated to the section overhead is greater than the number ofdata communications channel bits inserted into a line overhead and spaceallocated to the line overhead.
 32. The network element of claim 31wherein the data communications channel bits inserted into the lineoverhead is zero.
 33. The network element of claim 31 wherein the frameif a SONET frame.
 34. The network element of claim 31 wherein the frameis an SDH frame.
 35. The network element of claim 31 wherein the networkelement is an add-drop multiplexer.
 36. The network element of claim 31wherein the network element is a regenerator.
 37. The network element ofclaim 31 wherein the network element is a digital cross-connect.
 38. Thenetwork element of claim 31 wherein the network element is an ATM overSONET network element.
 39. A framer for constructing a frame having asection overhead and a line overhead, comprising: a processor forinserting into a frame a payload and for inserting into the frame aplurality of data communications channel bits; wherein the number ofdata communications channel bits inserted into a section overhead andspace allocated to the section overhead is greater than the number ofdata communications channel bits inserted into a line overhead and spaceallocated to the line overhead.
 40. A framer for constructing a framehaving a section overhead and a line overhead, comprising; a firstprocessor for inserting into a frame a payload; and a second processorfor inserting into the frame a plurality of data communications channelbits; wherein the number of data communications channel bits insertedinto a section overhead and space allocated to the section overhead isgreater than the number of data communications channel bits insertedinto a line overhead and space allocated to the line overhead.
 41. Anetwork using a frame having a section overhead and a line overhead,comprising; at least one line terminating equipment including aprocessor for inserting into a frame a payload and for inserting intothe frame a plurality of data communications channel bits, wherein thenumber of data communications channel bits inserted into a sectionoverhead and space allocated to the section overhead is greater than thenumber of data communications channel bits inserted into a line overheadand space allocated to the line overhead; and at least one sectionterminating equipment including a processor for inserting into a frame apayload and for inserting into the frame a plurality of datacommunications channel bits, wherein the number of data communicationschannel bits inserted into a section overhead and space allocated to thesection overhead is greater than the number of data communicationschannel bits inserted into a line overhead and space allocated to theline overhead.
 42. A network element for constructing a frame having asection overhead and a line overhead, comprising. a processor forinserting into a frame a plurality of payload bits and for insertinginto the frame a plurality of data communications channel bits, whereinthe number of data communications channel bits inserted into a sectionoverhead and space allocated to the section overhead is greater than thenumber of data communications channel bits inserted into a line overheadand space allocated to the line overhead.
 43. A network element forconstructing a frame having a section overhead and a line overhead,comprising: a first processor for inserting into a frame a plurality ofpayload bits; and a second processor for inserting into the frame aplurality of data communications channel bits; wherein the number ofdata communications channel bits inserted into a section overhead andspace allocated to the section overhead greater than the number of datacommunications channel bits inserted into a line overhead and spaceallocated to the line overhead
 44. A method for adapting to dual modesin a communications channel comprising the steps of: inserting into aframe a plurality of data communications channel bits, wherein thenumber of data communications channel bits inserted into a sectionoverhead is greater than the number of data communications channel bitsinserted into a line overhead; inserting into a frame a plurality ofdata communications channel bits, wherein the number of datacommunications channel bits inserted into a line overhead is greaterthan the number of data communications channel bits inserted into asection overhead; selecting between the steps of inserting into a framea plurality of data communications channel bits, wherein the number ofdata communications channel bits inserted into a section overhead isgreater than the number of data communications channel bits insertedinto a line overhead; and inserting into a frame a plurality of datacommunications channel bits, wherein the number of data communicationschannel bits inserted into a line overhead is greater than the number ofdata communications channel bits inserted into a section overhead. 45.The method of claim 44, wherein the frames are SONET frames.
 46. Themethod of claim 44, wherein the frames are SDH frames.
 47. The method ofclaim 44, wherein the number of data communications channel bitsinserted into a section overhead is greater than the number of datacommunications channel bits inserted into a line overhead, wherein thenumber of data communication bits inserted is zero.